The present invention relates to an one-directional or two-directional actuator used a shape memory alloy and a display conversion device of signs used this actuator.
One directional actuators of this type are constituted to allow a movable body workable in one direction to work by the restoration force to the memorized shape of shape memory alloy at the time of temperatuer rising and are proposed to use, for example, for the automatic opening of flue gas duct at the time of fire etc.
Moreover, two-directional actuators used the shape memory alloy are constituted from a movable body provided so as to work in two directions with in a fixed range, a shape memory alloy provided so as to allow said movable body to work in one direction by the restoration force to the memorized shape at the time of temperature rising and a bias spring or a weight allowing said movable body to work in other direction by exerting the bias force at the time of temperature lowering when said shape memory alloy becomes soft, and are used for the automatic opening and shutting of ventilating window etc., top and bottom switching of air conditioner serving for both cooling and heating and of louver, and the like.
Said movable body is allowed to work in the direction of restoration thereof from a point of time when the restoration force of the shape memory alloy becomes more than the bias force due to the spring or the weight between a time when the temperature at a position of the installation of actuator reaches a temperature at which the shape memory alloy beings to be transformed to the austenite phase (hereinafter referred to as "As point") and a time until it rises to a temperature at which the transformation to the austenite phase completes (hereinafter referred to as "Af point"), and it is allowed to work in the acting direction of the bias force from a point of time when said bias force becomes more than the force of the shape memory alloy between a time when the temperature at said position of the installation is lowered to a temperature at which the shape memory alloy begins to be transformed to the martensite phase (hereinafter referred to as "Ms point") and a time until it falls to a temperature at which the transformation to the martensite phase completes (hereinafter referred to as "Mf point").
The shape memory alloy repeats the transformation to the austenite phase and that to the martensite phase according to the change in temperature and allows various ones as described above to be driven by the restoration force when transformed to the austenite phase. In the case of rapid change in temperature, the transformation progresses rapidly, but, in the case of slow change in temperature such as the change in air temperature for example, the transformation progresses gradually.
And, in the cases of flue gas duct etc., it is desirable for them to be opened at a stroke when rising to a fixed temperature. With the conventional one-directional actuators, however, the working is slow so long as the temperature rising is not steep. Thus, when using them, for example, for the opening of flue gas duct etc., it is sometimes impossible to open the duct at a stroke.
Moreover, when applying the actuator used the shape memory alloy to the driving for the display conversion device of road signs as proposed previously by the inventors (Japanese Utility Model Application No. Sho 62-120,196), for example, when converting from a display of "Run with Care" to "Beware of Freezing" at a temperature lower than a certain temperature and converting this to the display of "Run with Care" at a temperature higher than a certain temperature, conventional two-directional actuators work only slowly according to the change in air temperature. As a result, the display cannot be converted at a stroke and no accurate display is made on the way of conversion causing a problem of half-finished display.
The purpose of the invention is to improve such a drawback of the actuator used the shape memory alloy and to provide an one-directional or two-directional actuator being made to work rapidly at a predetermined temperature even when the change in temperature is slow.
Moreover, the shape memory alloys have a common characteristic that there are gaps of temperature between As point and Mf point and between Af point and Ms point (this is said as "temperature hysteresis") as exemplified, for example, in FIG. 32.
Since no measures are taken to said temperature hysteresis with conventional actuators of this type, there has been a drawback that the temperature to allow the movable body to work in one direction is different from that to allow it to return in other direction due to that the temperature at which the restoration force and the bias force are balanced in the process of the shape memory alloy being transformed to the austenite phase and the temperature at which the force of alloy becoming weak in the process being transformed to the martensite phase and the bias force are balanced are different from each other.
That is to say, in the example of FIG. 32, if the temperature at which the force generated on the shape memory alloy at the time of temperature rising and the bias force are balanced is Tw, the temperature at which the decreasing force of said shape memory alloy at the time of temperature lowering and the bias force are balance will become T.
In addition, from the same reason, the temperature to allow the movable body to work in one direction and that to allow it to return in other direction cannot be adjusted arbitrarily.
The invention has also a purpose to mechanically solve the problem due to the temperature hysteresis aforementioned and to provide an actuator of improved type with which the working temperature of movable body to both directions can be adjusted arbitrarily and easily within a range after the force of the shape memory alloy and the bias force have been balanced.